In a superjunction lateral insulated gate bipolar transistor (LIGBT), electrons and holes participate in conduction at the same time. These two carriers form conductance modulation, which greatly reduces the specific on-resistance of the device. The chip region occupied by the device is reduced, and the typical structure can be referred to the transistor structure shown in FIG. 1. However, in devices fabricated with bulk silicon-based substrates, carriers can enter the lightly doped substrate to form unbalanced carriers. In this way, it takes a certain time to extract these carriers when the device is turned off, which increases the turn-off time and increases the power consumption.
At present, the most common solution is to use silicon-on-insulator (SOI) substrate instead of a bulk silicon substrate. As shown in FIG. 2, an insulator, which is typically a silica material, is inserted between the superjunction structure portion and the lightly doped substrate. The insulator layer can effectively block carriers from entering the lightly doped substrate, thereby avoiding the extraction of carriers in the lightly doped substrate during turn-off, shortening the turn-off time and reducing the turn-off power consumption. However, this solution has the disadvantages that the SOI substrate process is complicated and the cost is several times that of the bulk silicon material.
Another solution is to use an insulating substrate instead of a bulk silicon substrate, such as a sapphire substrate. As shown in FIG. 3, a semiconductor superjunction structure is fabricated on an intrinsic sapphire substrate. The intrinsic sapphire substrate is non-conductive and is a good insulator, so that the carriers in the semiconductor superjunction structure do not enter the intrinsic sapphire substrate, thus avoiding the extraction of carriers in the substrate during turn-off. Accordingly, the superjunction LIGBT fabricated on an insulating substrate such as sapphire has a short turn-off time and a low off-power consumption. However, the cost of the sapphire substrate in this solution is higher.
In summary, in the prior art, an insulator layer is inserted between the superjunction structure portion and the lightly doped substrate or the insulator substrate is directly used instead of the bulk silicon substrate to solve the problem that carriers in the LIGBT device will enter the lightly doped substrate. However, these solutions will lead to the problem of long turn-off time and high power consumption of the device, and cannot effectively cope with complicated process and high cost of the insulating substrate.